diff --git a/sys/include/net/coap.h b/sys/include/net/coap.h
index 275510463d51..06fe6b9b5df8 100644
--- a/sys/include/net/coap.h
+++ b/sys/include/net/coap.h
@@ -539,6 +539,7 @@ typedef enum {
  * @brief   Marks the boundary between header and payload
  */
 #define COAP_PAYLOAD_MARKER      (0xFF)
+#define COAP_PAYLOAD_MARKER_SIZE (1U)   /**< Size of the payload marker */
 
 /**
  * @defgroup net_coap_conf    CoAP compile configurations